1. Field of the Invention
The present invention relates to a honing tool attached to the distal end of a spindle (the output shaft) of a honing machine for rotation and forward and backward movements along axial directions to hone the inner surface of a workpiece to be ground.
2. Description of the Related Art
One of conventional honing tools for a honing machine is shown in FIG. 1 where a group of bar-like grinding stones 32 are mounted on the outer side of a cylindrical body 31 so as to extend radially and outwardly. More specifically, the bar-like grinding stones 32 of the honing tool are arranged for moving to and from the outer side of the cylindrical body 31 along radial directions. Each bar-like grinding stone 32 has a couple of arm-like supports 33 and 34 mounted on upper and lower regions thereof and inserted at the other end into corresponding slits provided in the wall of the cylindrical body 31 for joining. The cylindrical body 31 has an inner shaft 35 accommodated in the inner space thereof for upward and downward movements. The inner shaft 35 has two cone tapered portions 36 and 37 thereof arranged for accepting directly with their tapered surfaces the distal ends of the supports 33 and 34 of each bar-like grinding stone 32. As the inner shaft 35 remains urged by a spring or a hydraulic pressure, its cone tapered portions 36 and 37 generate forces for pushing the bar-like grinding stones 32 radially and outwardly from the cylindrical body 31. As a result, the bar-like grinding stones 32 come into direct contact with the inner surface of a workpiece to be ground and when is rotated and moved upward and downward along the axial direction, can hone the inner surface of the workpiece.
However, such a conventional honing tool is disadvantageous in that the bar-like grinding stones 32 which are held by the supports 33 and 34 shaped relatively thin and inserted into the corresponding slits in the wall of the cylindrical body 31 as arranged movable radially about the outer side of the cylindrical body 31 may possibly oscillate forward and backward, leftward and rightward, or upward and downward when rotated and moved upward and downward at the same time during the grinding. This will decline the parallelism between the contact surface of the bar-like grinding stones 32 and the ground surface of the workpiece, thus lowering the straightness and the dimensional accuracy of the workpiece and injuring the bar-like grinding stones 32. Also, in case that the workpiece has lands thereof defined by circumferential grooves in the inner surface thereof, each edge of the lands may be made blunt by the oscillation, hence permitting no highly accurate level of the honing process.
A honing tool according to the present invention is provided comprising a cylindrical body having a large-diameter portion provided at the distal end thereof; a tapered rod inserted into the inner bore of the cylinder body for sliding movements; and a plurality of grinding stones mounted to the large-diameter portion and urged radially by a pressing force of the tapered rod, wherein the large-diameter portion has a plurality of stone holding recesses provided radially therein from the inner bore to the outer edge for slidably holding the grinding stones, so that an upper guiding facet and a lower guiding facet are formed at the top side and the bottom side of each stone holding recess, respectively while a couple of side guiding facets are formed at both sides of the stone holding recess, and each of the grinding stones held in the corresponding stone holding recesses has an upper sliding facet and a lower sliding facet provided on the top side and the bottom side thereof, respectively for sliding directly on their respective upper and lower guiding facets while it has a couple of side sliding facets provided on both sides thereof for sliding directly on their respective side guiding facets and a tapered facet provided at an upper region thereof at the inner bore side for receiving the pressing force of the tapered rod.
The honing tool may be modified in that the grinding stone is arranged with the lowermost end of its grinding stone tip extending to be flush with the bottom of the large-diameter portion. Also, the large-diameter portion may have four of the stone holding recesses provided radially and spaced at intervals of 90 degrees and the grinding stones are slidably held in their respective stone holding recesses. The large-diameter portion may have a bottom plate fixedly joined by retaining screws to the bottom thereof for serving as the lower guiding facets.
In practice, the honing tool is attached to the distal end of the spindle of a honing machine which can rotate and reciprocate while the tapered rod accommodated in its cylindrical body is joined to the distal end of a pressing shaft installed in the spindle. During the honing process, the honing tool is driven by a rotating mechanism and a high-speed reciprocating mechanism for rotating motion and axial reciprocating motion at small pitches and moved forward by the action of an axially moving mechanism into a workpiece to be ground. As a result, a plurality of grinding stones provided on the large-diameter portion can grind the inner surface of the work piece while being pressed against the same.
At the time, as the grinding stone slidably held in the corresponding stone holding recess in the large-diameter portion is slid directly with its upper sliding facet on the upper guiding facet, with its lower sliding facet on the lower guiding facet, and with its side sliding facets on the side guiding facets at the stone holding recess, it can stably be held at the four sides without any jerky motion. Accordingly, the grinding stone can be driven for repeatedly rotating and reciprocating actions for grinding as being pressed against the inner surface of a workpiece, hence providing favorable accuracy of the roundness, the straightness, and the parallelism on the finished surface of the workpiece.
As the honing process is proceeded, the honing tool moves and grinds the inner surface of the workpiece until its reaches the lowermost end. Because the grinding stones are extended to be flushed at the lowermost end with the bottom of the large-diameter portion of the cylindrical body, they can completely reach the edge of the lowermost end of the workpiece. This permits the workpiece to be ground to the edge of its lowermost end at a higher accuracy of the straightness.
It is an object of the present invention to provide a honing tool which has the foregoing arrangement for stably holding its grinding stones without permitting any vibration or rocking and can thus perform a high level of the honing process at a desired straightness.